Area Forecast Discussion
Issued by NWS Wilmington, NC

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838 FXUS62 KILM 060812 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 312 AM EST Tue Dec 6 2016 .SYNOPSIS... A strong storm system will bring periods of heavy rainfall through today. Dry and seasonable weather will follow for mid- week ahead of an arctic front which will cross offshore late Thursday. Very cold temperatures will follow for Friday and Saturday. A warming trend will begin Sunday. && .NEAR TERM /THROUGH TONIGHT/... A powerful southern stream shortwave will eject out of South Texas this evening and become negatively tilted across the southern Mississippi Valley overnight. Surface cyclogenesis that is ongoing across across the northwest Gulf of Mexico will gradually translate to a classic Miller Type-B scenario early Tuesday with primary low pressure moving into Tennessee and secondary low pressure developing off the South Carolina coast along a sharpening coastal front. Impressive QG-forcing coupled with pwats surging to near 2.0 inches (well above normal for early December) will support a large swatch of moderate to locally heavy rains encompassing all of Southeast North Carolina and Northeast South Carolina for much of the nighttime period. Already seeing scattered showers developing across the southern Savannah River valley along the nose of a strengthening 850 hPa low- level jet. This activity will move into the southern and southwestern zones by early evening with steadier rains blossoming over the area shortly thereafter. Forecasting temperatures tonight is proving tricky with the high pressure wedge likely to hold firm for much of the night, except across the far south and along the coast where temperatures could rise begin to rise closer to sunrise as the coastal front begins to lift north/inland. With dewpoints holding in the upper 40s this afternoon, there will likely be some diabatic cooling at the onset of light rain, which will help drive temperatures down this evening before leveling off. Favored lows from the upper 40s northern areas (best potential for a longer duration of diabatic cooling) to the mid 50s elsewhere. The rain could become locally heavy at times, especially along the coast and across the central/southern zones where pwats will peak near 2.0 inches. There are no real concerns for flash flooding, but minor flooding of low-lying and poor drainage areas could occur in areas that typically flood such as Georgetown. The combination on intense forcing and some mid- level instability advecting into southern South Carolina could support a few elevated tstms overnight, roughly along/south of a Wilmington-Florence line. No severe weather is anticipated tonight. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... A deep layer ridge hangs on over the region through Wednesday night, then shifts south and east as the next upper trough moves into the Ohio River Valley. This upper trough will move into the eastern U.S. Thursday, then the axis will shift offshore later Friday. At the surface, high pressure will start off centered northeast of the area on Wednesday, then shift south over the area on Thursday and then south Thursday night. By Friday, a strong cold front is expected to push through the region. Models have not been very aggressive with producing any significant precipitation with this front. In fact, the latest ECMWF barely has any precipitation at all. Have continued slight chance to very low end chance pops, mainly over SC where best moisture, upper forcing and low level convergence will combine. Any precip should be short lived and confined to near the surface front. Clearing, cooler and breezy later Friday morning and afternoon behind the front. There is some potential for at least patchy fog Wednesday night given the surface ridge will be centered east-west over the area. Thus, have put patchy fog in the grids for Wednesday night. Temperatures will remain above normal through Thursday night, with highs in the lower 80s, and lows in the upper 50s to lower 60s. By Friday, much cooler, with highs likely struggling to reach 70 most areas. These cooler temperatures, combined with breezy northerly winds, will make it feel a little brisk. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 300 AM Tuesday...Very cold temperatures greet the extended as an arctic front will be well offshore Friday morning. Highs and lows Fri/Sat will be 10-15 degrees below climo, peaking in the upper 40s both aftns, and dropping into the low 20s by Saturday morning. This will be the coldest air since last winter, and gusty winds Friday will create an even more significant "bite" to the air despite full sunshine. The cold Canadian high pressure responsible for this chill will push offshore quickly by Sunday thanks to broad cyclonic flow aloft, setting up a warming trend back to seasonable values Sunday and into early next week. As this high moves offshore, return flow develops, and a weak coastal trough may develop offshore, advecting warm and moist air into the region for Monday ahead of a rapidly approaching cold front for Monday night. This will allow Monday to warm to above seasonable temps, but at the same time rain chances will increase ahead of the front late on Monday. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... As of 06Z...High confidence in IFR overnight, and persisting through much of this valid period. Low pressure consolidating near Florida will ride up a stalled front just offshore through this period, creating widespread rain, heavy at times. IFR cigs are slowly advancing NE tonight, and will envelop all terminals in the next few hours. Once this occurs, cigs will slowly lower, and LIFR is forecast much of Tuesday. VSBYS will fluctuate considerably during periods of heavier rainfall, but MVFR is forecast to be predominant. Winds will increase from the NE overnight to 10-15 kts, but will then back to the NW as the low pulls away during Tuesday, driving the front offshore. This wind shift will create subtle dry advection, and cigs will gradually improve late Tuesday, with VFR possibly developing inland by the end of this valid period. Extended Outlook...Fog possible Tuesday and Wednesday nights. VFR conditions expected to prevail late week through this weekend. && .MARINE... NEAR TERM /THROUGH TONIGHT/... North winds will veer to the northeast tonight as low pressure develops along a sharpening coastal front. A tightening pressure gradient between the low and high pressure to the north will support increasing winds, especially from Murrells Inlet north to Surf City. There are signals that winds could reach as high as 20-25 kt at times per the latest GFS and to some extent the NAM, but the various high resolution models are showing just a tad weaker low-level wind field. Will cap winds at 20 kt for now and per coordination with WFO Morehead City, a Small Craft Advisory will not be issued. Concerns will be passed on to WFO Wilmington after service backup concludes. Seas will build overnight, reaching 3-5 ft, except 2-3 ft over northern portions of Long Bay downwind of Cape Fear. Rain could locally reduce vsbys to less than 1 nm at times. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... No highlights expected through Thursday night. High pressure will shift from northeast of the area Wednesday to south of the area by later Thursday. Winds east-northeast Wednesday, becoming variable Thursday, then southwest Thursday night. Winds generally 15 knots or less and seas 4 feet or less. LONG TERM /FRIDAY THROUGH SATURDAY/... As of 300 AM Tuesday...SCA conditions possible to greet Friday morning as an arctic front will be positioned well offshore. In the wake of this front early Friday, NW winds of 20-25 kts will push seas up to 4-6 ft, and an SCA may be required. These winds and elevated seas will fall through Friday however as high pressure builds eastward. As this surface high moves eastward and offshore the Mid-Atlantic region during the wknd, winds will weaken to around 10 kts by late Saturday, with a slow veering to the NW. Seas fall quickly late Friday and on Saturday as well, from 3-5 ft Friday aftn to just 1-2 ft at the end of the period. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until noon EST Wednesday for AMZ250-252- 254-256. && $$ SYNOPSIS...JDW NEAR TERM...99 SHORT TERM...99 LONG TERM...JDW AVIATION...JDW MARINE...99/JDW

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